Testing of visual acuity, contrast sensitivity and sensitivity to disability glare have traditionally needed assistance from test personnel and manual interpretation of the test subject's answers and manual reporting. While automating the test procedure it is important that the tests are reliable, fast and that they won't require continuous assistance or manual reporting work from test personnel.
Most common psychometric tests are different multiple-alternative forced-choice methods. In these a person has to identify a symbol of variable size, contrast or color visible on the display unit with or without glare light. The problem with these methods is that in order to compensate for the differences between aggressively guessing test subject and cautious test subject, the test subject is forced to guess even when the symbol is not seen. Therefore, test subject can very often correctly guess the symbol even without seeing it correctly. To decrease the effects of guessing more alternatives and more test steps are required for a reliable estimation of the threshold of vision. Increasing the amount of alternatives makes the test more demanding to operate for the test subject and stressful for the test subject.
E.g. in the Freiburg Visual Acuity test variable size or contrast Landolt C or tumbling E symbols (optotypes) are presented on a monitor in one of several orientations: This is adjustable, but eight orientations are referred to in the literature to be needed for repeatable results. The person presses one of eight buttons which are arranged according to the eight possible positions of the symbols. To estimate the acuity threshold the responses on the buttons are recorded and a mathematical model determines the result. The patient should guess the symbol direction if she/he is not sure of it. Measurement terminates after a fixed number of trials, or after a number of threshold crossing, or after another criteria.
U.S. Pat. No. 4,861,156 describes a visual acuity test procedure using a video capable of presenting and projecting means and a control unit. GB 2,397,391 discloses a visual acuity computerized test utilizing a remote control unit. WO 2008081446 A2 describes a method, algorithm and device for testing visual acuity. In US 2004/105073 a threshold value in testing of visual acuity is determined.